Sorry, missed the RAW file. So I downloaded it and played with it a bit.
The rendering of the flower petals in the Classic working color space is more yellow. But red is very clipped - that is, out of gamut. With the DxO Wide Gamut WCS, raise “Protect saturated colors” in the Color Rendering palette. That will reduce red enough to see the yellows. Especially if you use DxO Camera Profile and not Neutral color, realistic tonality. (The former converts the color data better for a display that isn’t wide-gamut such as sRGB.) I’ve concluded that this approach lets PhotoLab do most of the work in converting a very saturated image for a smaller color space.
If you don’t do this, then red has to be managed through other adjustments. Turning on Soft Proofing for sRGB will tame it a bit, but not as well as if you use the Protect saturated colors adjustment in the Color Rendering palette. To see what I mean, turn on the destination gamut warning, select the red channel in the HSL tool, and lower the saturation.
The yellows aren’t as vibrant as with the Classic WCS, though. I’m still playing to see if there’s a way to more closely approximate the Classic rendering for sRGB. But it isn’t straightforward.
UPDATE: I raised the Rendering intensity in the Color Rendering palette to 200 (with Protect saturated colors set to an intensity of 67). This made the flower more orange (taming red), but darkened the background. Weird as it is to set the intensity so high, I think the overall tonality and color preservation are now far superior to the Classic WCS version. Give it a try and see what you think.
It seems using the HSL to try to intensify orange or yellow doesn’t work, because it’s the red that’s the problem.